Seized 102 power head

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african imp
Posts: 395
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Location: Hout Bay

Re: Seized 102 power head

Post by african imp » Wed Feb 20, 2019 7:15 am

A spare piston ring I have fits well enough.

The hand book says the rings end gap should be 0.004" the gap on my spare ring can barely be seen, so if I need to use these rings I need to open the end gaps some.

Is there a Top ring, they both look the same to me.

The top of the compression bowl is mainly clean cast iorn, I think that this motor has run for very few hours?
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Last edited by african imp on Wed Feb 20, 2019 8:44 am, edited 4 times in total.

african imp
Posts: 395
Joined: Thu Jan 03, 2019 5:44 am
Location: Hout Bay

Re: Seized 102 power head

Post by african imp » Wed Feb 20, 2019 7:27 am

The old piston that I was able to remove and save its piston rings from does not have the black iorn inserts, which has the stop that restricts the rings from turning, why are the two pistons different?

Are the rings interchangable?
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Last edited by african imp on Wed Feb 20, 2019 8:45 am, edited 1 time in total.

african imp
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Re: Seized 102 power head

Post by african imp » Wed Feb 20, 2019 8:41 am

The spare piston ring shows hardly any gap in the ends, it is at the lower side of the bore.

The combustion chamber has very little carbon in it, I see mainly clean cast iorn, I aasume the bore sleeve is a steel insert?

Apart from using a clean dry cloth I have not cleaned the bore in anyway.
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Horsley-Anarak
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Re: Seized 102 power head

Post by Horsley-Anarak » Wed Feb 20, 2019 6:53 pm

african imp wrote: I aasume the bore sleeve is a steel insert?

That is a new one for me, have never seen a sleeved 102, what makes you think it has a steel liner.

Dingleberry hone, gap the rings and you should be good to go. Make sure piston is the correct way up.

blokewithaboat
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Re: Seized 102 power head

Post by blokewithaboat » Wed Feb 20, 2019 8:27 pm

New one on me too.

Not that i've seen any of the newer style 102 cylinders with the narrow transfer port and centrally mounted carb, as most of my interests are with the older pre 1960 engines and older.


I can't put my finger on it right now but something is not right with this power head.
Bent con-rod maybe? (can you see a number cast into the con-rod Roy?)
Piston out of shape somewhere? Any unusual scuff marks on the piston skirt or the cylinder bore.
Can't be the rings as these look pristine and not seized to me. Yes the rings are inter changeable by the way. They will only fit one way up against the small locating post in the ring groove. Magnifying glass helps to see the orientation here. Suffice to say you can fit either ring in either ring groove, doesn't matter.
The bore (going by the picture) looks as new with little to no scoring that i can see so all good there. Piston ring end gap is small and often difficult to determine exactly, just as long as there is a gap and it's not too small. Thermal expansion will soon tell if it's too tight. Go too big with the gap and you could lose some compression until the engine has warmed up a bit so gently does it here.
Is the crank shaft running true? Not bent anywhere?

Seems odd that the piston would move freely inside the bore but only in certain places! Towards the bottom of the piston's travel inside the bore is where Roy has experienced something not quite right when extracting the piston assembly, so with that being said i would measure the cylinder bore with a micrometer and see if there's any variance compared to the seagull manuals measurements. Measure the bore at several points along the bore's length and see if they all fall within the same ballpark. If there's much wear at all i'd expect it to be towards the top of the cylinder at the combustion chamber end and NOT the bottom of the cylinders bore.

While you have it apart like this it might be a good time to gently clean the piston skirt with something non-abrasive and see if this helps any. Go round the ring grooves as well if you can. While you're at it, take the rest of the crankcase assembly apart for a careful examination. Woodruff key for the flywheel is easily removed with a pair of wire cutters gripped along its length and lever it out against the side of the crank then its just 5 bolts and its apart with a gentle tap. Look for any blueing in the running surfaces of the bushes/bearings on the crank and the con-rod. Look for any scuff marks on the piston skirt too as this might help point us in the right direction of our culprit.

Let us know what you find Roy

african imp
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Re: Seized 102 power head

Post by african imp » Thu Feb 21, 2019 7:24 am

Thanks for the replies and comments.

With the orignal piston removed from the bore, I have tested the fit with a spare pistion, the rings from it are really good, the piston is not. as the groove are shot.

I have had the original piston in an oxalic acid solution since yesterday to assist with freeing the rings off.

The piston from the engine has the top ring fully seized in its groove, the second ring is now free, I will work on top ring over the next few days to free it off and reuse.

The piston fits the bore fine now it has been removed, it stops at the rings of course.

The crank case assembly is like new?
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african imp
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Re: Seized 102 power head

Post by african imp » Thu Feb 21, 2019 7:50 am

Horsley-Anarak wrote:
african imp wrote: I aasume the bore sleeve is a steel insert?
That is a new one for me, have never seen a sleeved 102, what makes you think it has a steel liner.

Dingleberry hone, gap the rings and you should be good to go. Make sure piston is the correct way up.
I assumed that as the cylinder bore sticks out of the block an eigth of an inch and the bore is then clean to the combustion chaber that is was a steel liner?

Your saying that this is not the case?

This is the first Seagull engine that I have removed a piston from, so things are new to me.

african imp
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Re: Seized 102 power head

Post by african imp » Thu Feb 21, 2019 11:54 am

The top ring was basically bonded into the groove with some sort of calcium, the ring would not come out without me breaking it.

I now need to give the groove a good clean, then fit a spare piston ring.
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Last edited by african imp on Thu Feb 21, 2019 2:20 pm, edited 1 time in total.

african imp
Posts: 395
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Re: Seized 102 power head

Post by african imp » Thu Feb 21, 2019 1:44 pm

If I assume that there has not been water in the engine and I see no sign of it, I have to think that whatever so called 2 stroke mix was in the engine and when it was run then stored, it then turned itself to a solid mass and went into a glue form and then turned hard, the top ring was in fact stuck into the piston groove.
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blokewithaboat
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Re: Seized 102 power head

Post by blokewithaboat » Thu Feb 21, 2019 8:00 pm

I do know that our american brethren suffer with problems with their fuel if left for long periods of time.
Something to do with the chemical makeup of the fuel itself.

I'm wondering if a similar problem exists in SA, hence the problem you've had with stuck piston rings. At least it was a fairly simple thing to put right.
I know it can be a problem over here too if fuel has been left for more than a year inside a carb it turns to gloop.
I'm currently rebuilding a set of carbs on my motorbike that hasn't run in 12 years, and you can imagine what a mess i found inside the float bowls can't you? The fuel tap was worse actually, seized solid from really thick tar like substance pretty much everywhere you looked. Gauze filters completely blocked up, same in the carbs too and there's 4 of them. :roll:

At least a seagull is fairly easy to work on compared to a 33 year old air cooled suzuki 750 sports bike.

african imp
Posts: 395
Joined: Thu Jan 03, 2019 5:44 am
Location: Hout Bay

Re: Seized 102 power head

Post by african imp » Fri Feb 22, 2019 11:09 am

blokewithaboat wrote:I do know that our american brethren suffer with problems with their fuel if left for long periods of time.
Something to do with the chemical makeup of the fuel itself.

I'm wondering if a similar problem exists in SA, hence the problem you've had with stuck piston rings. At least it was a fairly simple thing to put right.
I know it can be a problem over here too if fuel has been left for more than a year inside a carb it turns to gloop.
I'm currently rebuilding a set of carbs on my motorbike that hasn't run in 12 years, and you can imagine what a mess i found inside the float bowls can't you? The fuel tap was worse actually, seized solid from really thick tar like substance pretty much everywhere you looked. Gauze filters completely blocked up, same in the carbs too and there's 4 of them. :roll:

At least a seagull is fairly easy to work on compared to a 33 year old air cooled suzuki 750 sports bike.
That sounds like you will be busy a long while?

Here we have ethanol added to the fuel, the rule is 5% max but who knows?

It can still melt some fuel lines?

I did it on a Hillman Imp rebuild, started the new 998cc engine I had just finished, I then went inside the house for lunch and when I came out a half hour later there was a smell of petrol that was by then on the floor from the Solex fuel bowl.

african imp
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Location: Hout Bay

Re: Seized 102 power head

Post by african imp » Fri Feb 22, 2019 11:18 am

Yesterdays images, I can now split the crankcase to re seal it and then put the engine back together.
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african imp
Posts: 395
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Location: Hout Bay

Re: Seized 102 power head

Post by african imp » Fri Feb 22, 2019 11:33 am

The hot water trick on the piston worked a treat to remove the gudgeon pin, I will be doing that again to replace the same pin soon.
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